fix OpenBSD cache memory information (#1542)
fix OpenBSD cache memory information (#1542)

This will now use `bcstats.numbufpages` instead of `uvmexp.vnodepages`.

Inspired by OpenBSD's `src/usr.bin/top`

Signed-off-by: Matthieu Guegan <88a5758e1efa2610ef7797ffdb7c51787b742514@deindeal.ch>
siavashs/node_exporter,prometheus/node_exporter,siavashs/node_exporter,siavashs/node_exporter,prometheus/node_exporter,prometheus/node_exporter,siavashs/node_exporter